LIFESTYLE FACTORS ASSOCIATED WITH MYOPIA IN SCHOOLCHILDREN

Boy wearing glasses holding mobile and carrying a backpack

While for many, myopia is an optically corrected inconvenience (1),  for an ever-increasing minority, myopia is a factor leading to more severe vision disorders and visual impairment in mid to later life (2). Myopia is a recognised growing health issue in East Asia, where large-scale measurement and monitoring first began in the 1980s, with a very high prevalence (80%–90%) in school leavers (3). The global myopia prevalence was estimated at two billion in 2010 and predicted to rise to five billion (half the projected world’s population) by 2050 (4).

The primary aim of the Ireland Eye Study was to report myopia prevalence in schoolchildren in Ireland. The study involved 1,626 schoolchildren from a mix of 37 urban/rural schools and schools in socioeconomically advantaged and disadvantaged areas throughout Ireland. All children had their eyes examined during the school day, and parents/guardians completed detailed questionnaires on diet and lifestyle. Sedentary lifestyle, obesity, increased screentime and reduced daylight exposure, in addition to family history, were associated with short-sightedness in these schoolchildren.

Some key findings included:

  • Screentime: Children using screens for more than three hours per day were almost four times more likely to be short-sighted than those spending less than one hour on screens daily. The relationship between increased time on screens and increased myopia prevalence may be due to several factors. The high accommodative demand associated with using smartphones at short working distances (5), cumulative blue light exposure (6), coupled with dim lighting resulting in dilated pupils and the resulting increased peripheral image defocus (7), plus the reduced time outdoors (8), may lead to increased risk of myopia onset or progression in susceptible children.
  • Obesity: Clinically obese children were close to three times more likely to be short-sighted than healthy-weight children. The cause is uncertain. What is known is that obesity is associated with reduced brain plasticity (9), increased metabolic disorders (10), diabetic retinopathy and peripheral artery disease where the tiny blood vessels supplying the eyes may be compromised (11). Further research is needed to unravel the relationship between BMI and myopia.
  • Physical activity: Children with sedentary lifestyles were almost three times more likely to be short-sighted than children involved in regular physical activities. Consequently, longitudinal research on whether engaging in after-school physical activities or not engaging in screen-based activities to prevent myopia progression is crucial.
Sedentary lifestyle, obesity, increased screentime and reduced daylight exposure, in addition to family history, were associated with short-sightedness in these schoolchildren.
  • Outdoor time: Children who spent less than one hour outdoors per day were five times more likely to be short-sighted than those spending more than four hours outdoors daily during summer. Whether increasing myopia prevalence is to do with less outdoor time or due to activities pursued indoors is a matter for speculation (12). Recent research demonstrated time outdoors >2.5 hours per day during daylight may postpone the onset of myopia and slow the myopic shift in refractive error (13); however, results regarding the effects of daylight exposure on myopia progression are equivocal. The mechanisms underpinning daylight exposure’s protective effect against myopia are unclear; increased depth of focus plus low accommodative demand associated with time spent outdoors has been proposed as possible biological mechanisms (14). Whether this is entirely due to the flat dioptric topography of the visual field outdoors (15), or due to increased light levels outdoors is inconclusive. The close link between circadian rhythms and eye growth and decreased sleep quality with later bedtimes in children with high myopia (16) further reinforces the part light exposure plays in refractive error development in children. Therefore, circadian timing and school hours may be essential factors to consider when addressing myopia control at a public health level.
  • Breastfeeding for the first three months of life appeared to have a protective effect against short-sightedness, with bottle-fed babies twice as likely to be short-sighted. Breastfeeding during infancy provides babies with polyunsaturated fatty acids, essential vitamins and bioactive components necessary for brain and retinal growth and maturation in infants (17). Long-chain polyunsaturated fatty acids are essential throughout the retina to support retinal structure and function, influencing visual development and eye growth (18).

One clear message today is the importance of daily outdoor physical activities and managing children’s screentime as a necessary part of children’s eye health. Tracking children’s eyesight over time will be essential to supplement these findings. More research examining the broader consequences of today’s ubiquitous media environment and, in particular, the effect this intense digital immersion may have on children’s health, and vision needs to be addressed as part of the broader public health education programme. Whilst many of the health benefits associated with increased physical activity, reduced screentime, and increased outdoor time may not manifest themselves until adulthood, the benefits at that time will be material with significant benefits for not only the individual but also the community in terms of independence and quality of life.

References:  

  1. McCrann S, Flitcroft I, Lalor K, Butler J, Bush A, Loughman J. Parental attitudes to myopia: a key agent of change for myopia control? Ophthalmic Physiol Opt. 2018;38(3):298-308. doi:10.1111/opo.12455
  2. Sankaridurg P, Tahhan N, Kandel H, et al. IMI Impact of Myopia. Invest Ophthalmol Vis Sci. 2021;62(5):2-2. doi:10.1167/IOVS.62.5.2
  3. Seet B, Wong TY, Tan DTH, et al. Myopia in Singapore : taking a public health approach. 2001:521-526
  4. Holden BA, Fricke TR, Wilson DA, et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016;123(5):1036-1042. doi:10.1016/J.OPHTHA.2016.01.006
  5. Oh JH, Yoo H, Park HK, Do YR. Analysis of circadian properties and healthy levels of blue light from smartphones at night. Sci Rep. 2015;5(1):11325. doi:10.1038/srep11325
  6. Hatori M, Gronfier C, Van Gelder RN, et al. Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies. npj Aging Mech Dis. 2017;3(1):9. doi:10.1038/s41514-017-0010-2
  7. Smith EL, Hung L-F, Huang J. Relative peripheral hyperopic defocus alters central refractive development in infant monkeys. Vision Res. 2009;49(19):2386-2392. doi:10.1016/j.visres.2009.07.011
  8. Read SA, Collins MJ, Vincent SJ. Light exposure and eye growth in childhood. Investig Ophthalmol Vis Sci. 2015. doi:10.1167/iovs.14-15978
  9. Sui SX, Ridding MC, Hordacre B. Obesity is Associated with Reduced Plasticity of the Human Motor Cortex. Brain Sci 2020, Vol 10, Page 579. 2020;10(9):579. doi:10.3390/BRAINSCI10090579
  10. De Rezende LFM, Lopes MR, Rey-Lopez JP, Matsudo VKR, Luiz ODC. Sedentary behavior and health outcomes: An overview of systematic reviews. PLoS One. 2014;9(8). doi:10.1371/JOURNAL.PONE.0105620
  11. Keller K, Hobohm L, Geyer M, et al. Obesity paradox in peripheral artery disease. Clin Nutr. 2019;38(5):2269-2276. doi:https://doi.org/10.1016/j.clnu.2018.09.031
  12. Ngo C, Saw SM, Dharani R, Flitcroft I. Does sunlight (bright lights) explain the protective effects of outdoor activity against myopia? Ophthalmic Physiol Opt. 2013;33(3):368-372. doi:10.1111/opo.12051
  13. Wu P-C, Chen C-T, Lin K-K, et al. Myopia Prevention and Outdoor Light Intensity in a School-Based Cluster Randomized Trial. Ophthalmology. 2018;125(8):1239-1250. doi:10.1016/j.ophtha.2017.12.011
  14. Pärssinen O, Hemminki E, Klemetti A. Effect of spectacle use and accommodation on myopic progression: Final results of a three-year randomised clinical trial among schoolchildren. Br J Ophthalmol. 1989;73(7):547-551. doi:10.1136/bjo.73.7.547
  15. French AN, Ashby RS, Morgan IG, Rose KA. Time outdoors and the prevention of myopia. Exp Eye Res. 2013;114:58-68. doi:10.1016/j.exer.2013.04.018
  16. Nickla DL. Ocular diurnal rhythms and eye growth regulation: Where we are 50 years after Lauber. Exp Eye Res. 2013;114:25-34. doi:10.1016/j.exer.2012.12.013
  17. Liu S, Ye S, Wang Q, Cao Y, Zhang X. Breastfeeding and myopia : A cross-sectional study of children aged 6 – 12 years in Tianjin, China. Sci Rep. 2018;(22):1-10. doi:10.1038/s41598-018-27878-0
  18. Gorusupudi A, Liu A, Hageman GS, Bernstein PS. Associations of human retinal very long-chain polyunsaturated fatty acids with dietary lipid biomarkers. J Lipid Res. 2016;57(3):499-508. doi:https://doi.org/10.1194/jlr.P065540

Doctor Síofra Harrington is a lecturer, researcher, clinical supervisor with the School of Physics and Clinical and Optometric Sciences at Technological University Dublin, Ireland. She is a fellow of the Association of Optometrists Ireland (AOI). Doctor Harrington is the principal investigator for the Ireland Eye Study, which reported the prevalence of ametropia, amblyopia, and vision impairment in schoolchildren in Ireland. Doctor Harrington is the first author of six peer-reviewed academic publications and numerous academic poster presentations reporting Ireland Eye Study findings.